Hello Mr Shankar.
Is the rash limited to one side of the body? If yes you may be suffering from Herpes ZOster
. It is a viral infection. It is basically the same virus which causes chicken pox
. After a CP attack the virus becomes dormant in the nerves and sometimes it gets reactivated to produce herpes zoster. As for the medication I presume you are being treated with acyclovir. You may also consider taking Gabapentin
after discussing with your dermatologist
, in case you still have pain.